The present invention relates to an aqueous dispersion of a substantially light-insensitive organic silver salt and a photosensitive silver halide and a photothermographic recording material prepared therefrom.
EP-A 754 969 discloses a process for producing a suspension of particles containing a substantially light-insensitive silver salt of an organic carboxylic acid, comprising simultaneous metered addition of an aqueous solution or suspension of an organic carboxylic acid or its salt; and an aqueous solution of a silver salt to an aqueous liquid, wherein the metered addition of the aqueous solution or suspension of the organic carboxylic acid or its salt; and/or the aqueous solution of the silver salt is regulated by the concentration of silver ions or the concentration of anions of the silver salt in the aqueous liquid. In preferred embodiments of this process after completion of the production of the aqueous suspension of the particles, excess dissolved silver ions are converted into at least one silver salt and the particles of substantially light-insensitive silver salt of an organic carboxylic acid are produced in the presence of silver halide particles.
EP-A 851 285 discloses a process for producing an aqueous dispersion I containing particles including a substantially light-insensitive organic heavy metal salt A with a solubility in 1 L of water of less than 10xe2x88x922 g at 20xc2x0 C. comprising the steps of: (i) producing an aqueous dispersion II containing particles including a salt B with a solubility in 1 L of water between 15 g and 0.01 g at 20xc2x0 C.; and (ii) converting the salt B in the particles of the aqueous dispersion II into the organic heavy metal salt A, characterized in that the organic heavy metal salt A and the salt B have a common cation.
It is known [see e.g. The Theory of the Photographic Process Fourth Edition, Ed. T. H. James, Eastman Kodak (1977), pages 157-158] that decreased coating pAg (=increased UAg) increases emulsion photosensitivity in conventional silver halide emulsion materials and that this effect is reversible i.e. increased coating pAg (=decreased UAg) reduces the photosensitivity in conventional silver halide emulsion materials. The addition of a soluble silver salt to a dispersion of photosensitive silver halide prior to coating produces a photographic material with a high fog level.
A principal problem in developing photothermographic recording materials with photo-addressable thermally developable elements coated from aqueous media is their lower photosensitivity than photothermographic recording materials with photo-addressable thermally developable elements coated from solvent media. A means is therefore necessary to boost the photosensitivity of photo-addressable thermally developable elements coated from aqueous media, so that the environmental and economic benefits of coating from aqueous media can be realized.
It is therefore an aspect of the invention to provide a means of increasing the photosensitivity of photothermographic recording materials coated from aqueous media.
It is therefore a further aspect of the invention to provide a photothermographic recording material with increased photosensitivity whose photo-addressable thermally developable element is coated from aqueous media.
It is therefore a further aspect of the invention to provide an aqueous dispersion for use in providing a photothermographic recording material with increased photosensitivity whose photo-addressable thermally developable element is coated from aqueous media.
It is therefore a still further aspect of the invention to provide a process for producing an aqueous dispersion for use in providing a photothermographic recording material with increased photosensitivity.
Further aspects and advantages of the invention will become apparent from the description hereinafter.
Whereas in convention photographic emulsions addition of a soluble silver salt to a dispersion of photosensitive silver halide prior to coating produces a photographic material with a very high fogging level, it has been surprisingly found that the addition of a silver salt with a water-solubility greater than 0.1 g/L water to an aqueous dispersion of a substantially light-insensitive and substantially water-insoluble organic silver salt, a photosensitive silver halide, and a binder increases the photosensitivity of a photo-addressable thermally developable element containing a reducing agent for the organic silver salt and a layer produced by coating the aqueous dispersion onto a support without increasing the background density of prints produced therewith.
The above mentioned aspects are realized by a process for producing an aqueous dispersion comprising in the following order the steps of: (i) preparing a dispersion of photosensitive silver halide and a binder or a surfactant in an aqueous medium; (ii) adding a first silver salt to the dispersion prepared in step (i); and (iii) adding a second silver salt to the dispersion prepared in step (ii), wherein the aqueous dispersion is substantially free of a water-soluble metal or ammonium salt of an aliphatic carboxylic acid with greater than 12 carbon atoms, the first silver salt is a substantially light-insensitive and substantially water-insoluble silver salt of an organic carboxylic acid, and the second silver salt has a water-solubility greater than 0.1 g in 1 L of water at 20xc2x0 C.
The above mentioned aspects are further realized by a process for producing an aqueous dispersion comprising in the following order the steps of: (i) preparing a dispersion of photosensitive silver halide and a binder or a surfactant in an aqueous medium; (ii) adding a second silver salt to the dispersion prepared in step (i); and (iii) adding a first silver salt to the dispersion prepared in step (ii), wherein the aqueous dispersion is substantially free of a water-soluble metal or ammonium salt of an aliphatic carboxylic acid with greater than 12 carbon atoms, the first silver salt is a substantially light-insensitive and substantially water-insoluble silver salt of an organic carboxylic acid, and the second silver salt has a water-solubility greater than 0.1 g in 1 L of water at 20xc2x0 C.
The above-mentioned aspects are also realized by an aqueous dispersion obtainable with either of the above-mentioned processes.
The above-mentioned aspects are also realized by the use of a second silver salt with a water-solubility greater than 0.1 g/L water at 20xc2x0 C. for increasing the sensitivity of a photothermographic recording material thermally developable under substantially water-free conditions, the photothermographic recording material having a photo-addressable thermally developable element, the photo-addressable thermally developable element containing a first silver salt, a reducing agent therefor in thermal working relationship therewith and a binder, wherein the aqueous dispersion is substantially free of a water-soluble metal or ammonium salt of an aliphatic carboxylic acid with greater than 12 carbon atoms and the first silver salt is a substantially light-insensitive and substantially water-insoluble silver salt of an organic carboxylic acid.
The above-mentioned aspects are also realized by a photothermographic recording material thermally developable under substantially water-free conditions, the photothermographic recording material comprising a support and a photo-addressable thermally developable element, the photo-addressable thermally developable element fulfilling two requirements:
(i) the photo-addressable thermally developable element contains a first silver salt as defined above, a reducing agent therefor in thermal working relationship therewith, a photosensitive silver halide and a binder; and
(ii) the photo-addressable thermally developable element comprises a layer obtainable by coating the above-mentioned aqueous dispersion onto the support.
The above-mentioned aspects are also realized by a process for preparing a photothermographic recording material thermally developable under substantially water-free conditions, the photothermographic recording material comprising a support and a photo-addressable thermally developable element and the photo-addressable thermally developable element containing a photosensitive silver halide, a first silver salt, a reducing agent therefor in thermal working relationship therewith and a binder, comprising the steps of: (i) coating the above-described aqueous dispersion onto a support; and (ii) drying the layer formed in step (i).
Further preferred embodiments of the present invention are disclosed in the dependent claims.
The term aqueous for the purposes of the present invention means containing at least 60% by volume of water, preferably at least 80% by volume of water, and optionally containing water-miscible organic solvents such as alcohols e.g. methanol, ethanol, 2-propanol, butanol, iso-amyl alcohol, octanol, cetyl alcohol etc.; glycols e.g. ethylene glycol; glycerine; N-methyl pyrrolidinone; methoxypropanol; and ketones e.g. 2-propanone and 2-butanone etc.
Substantially free of a water-soluble metal or ammonium salt of an aliphatic carboxylic acid with greater than 12 carbon atoms means that a water-soluble metal or ammonium salt of an aliphatic carboxylic acid with greater than 12 carbon atoms is not intentionally present and if present is only present in trace quantities.
The term water-soluble salt means salts with a solubility in water at 20xc2x0 C. of at least 2 mg/L. The term metal or ammonium salt of an aliphatic carboxylic acid with greater than 12 carbon atoms, includes lithium, potassium, sodium, rubidium, caesium and ammonium salts of aliphatic carboxylic acids, such as behenic and stearic acid, and mixtures thereof.
Substantially light-insensitive means not intentionally light sensitive and resistant to darkening upon exposure.
Substantially water-insoluble means a solubility in water at 20xc2x0 C. of less than 2 mg/L.
S is defined as that exposure in mJ/m2 at which the photothermographic recording material attained an optical density of 1.0 above Dmin. Thus the lower the value of S, the higher the photosensitivity of the photothermographic recording material.
The UAg of an aqueous liquid is defined in this specification as the potential difference between a silver electrode (of 99.99% purity) in the aqueous liquid and a reference electrode consisting of a Ag/AgCl-electrode in 3M KCl solution at room temperature connected with the liquid via a salt bridge consisting of a 10% KNO3 salt solution.
By the term xe2x80x9cheat solventxe2x80x9d in this specification is meant a non-hydrolyzable organic material which is in solid state in the recording layer at temperatures below 50xc2x0 C. but becomes a plasticizer for the recording layer in the heated region and/or liquid solvent for at least one of the redox-reactants, e.g. the reducing agent for the first silver salt, at a temperature above 60xc2x0 C.
By thermally developable under substantially water-free conditions as used is the present specification, means heating at a temperature of 80xc2x0 to 250xc2x0 C. under conditions in which the reaction system is approximately in equilibrium with water in the air, and water for inducing or promoting the reaction is not particularly or positively supplied from the exterior of the thermographic recording material. Such a condition is described in T. H. James, xe2x80x9cThe Theory of the Photographic Process, Fourth Edition, Macmillan 1977xe2x80x9d, page 374.
The first silver salt is a substantially light-insensitive and substantially water-insoluble silver salt of an organic carboxylic acid having as its organic group: aryl, aralkyl, alkaryl or alkyl groups. Aliphatic carboxylic acids known as fatty acids, wherein the aliphatic carbon chain has preferably at least 12 C-atoms, are preferred e.g. silver laurate, silver palmitate, silver stearate, silver hydroxystearate, silver oleate, silver behenate and silver arichidate, which silver salts are also called xe2x80x9csilver soapsxe2x80x9d. Other silver salts of an organic carboxylic acid as described in GB 1,439,478, e.g. silver benzoate, and silver salts of organic carboxylic acids described in Research Disclosure 17029, but excluding silver salts of organic carboxylic acids substituted with a heterocyclic thione group as disclosed in Research Disclosure 12542 and U.S. Pat. No. 3,785,830, may also be used to produce a thermally developable silver image. Combinations of the first silver salts may also be used in the present invention. Aqueous dispersions of first silver salts or mixtures thereof can be produced as described in U.S. Pat. No. 5,891,616 and EP-A 848286 and U.S. Pat. No. 3,839,049.
The second silver salt in the aqueous dispersion of the present invention has a solubility in water at 20xc2x0 C. of greater than 0.1 g/L, with greater than 1 g/L being preferred.
Suitable second silver salts in the aqueous dispersion of the present invention include silver nitrate, silver acetate, silver propionate, silver butyrate, silver isobutyrate, silver tartrate, silver salicylate, silver malonate, silver succinate, silver lactate and silver oxalate. The solubilities of some of these salts are given below:
Silver salts marked with # are themselves photosensitive although no deterioration in the level of image background has been observed upon adding the second silver salt, when such salts are used.
It is known in silver halide photography that addition of soluble silver salts to a dispersion of a silver halide produces an increase in UAg (=decrease in pAg=an increase in free silver ion concentration), which can result in partial reduction of the silver salts present, thereby producing metallic silver nuclei. Such metallic silver nuclei give rise to an increased fogging level in silver halide photographic materials. It is possible that an analogous effect is the basis for the sensitivity increase arising from the present invention.
The photosensitive silver halide used in the present invention may be employed in a range of 0.1 to 100 mol percent; preferably, from 0.2 to 80 mol percent; particularly preferably from 0.3 to 50 mol percent; especially preferably from 0.5 to 35 mol %; and especially from 1 to 12 mol % of substantially light-insensitive organic silver salt.
The silver halide may be any photosensitive silver halide such as silver bromide, silver iodide, silver chloride, silver bromoiodide, silver chlorobromoiodide, silver chlorobromide etc. The silver halide may be in any form which is photosensitive including, but not limited to, cubic, orthorhombic, tabular, tetrahedral, octagonal etc. and may have epitaxial growth of crystals thereon.
The silver halide used in the present invention may be employed without modification. However, it may be chemically sensitized with a chemical sensitizing agent such as a compound containing sulphur, selenium, tellurium etc., or a compound containing gold, platinum, palladium, iron, ruthenium, rhodium or iridium etc., or a combination thereof. The details of these procedures are described in T. H. James, xe2x80x9cThe Theory of the Photographic Processxe2x80x9d, Fourth Edition, Macmillan Publishing Co. Inc., New York (1977), Chapter 5, pages 149 to 169.
The grain size of the silver halide particles can be determined by the Moeller Teller method in the sample containing silver halide particles is sedimented upon a filter paper, which is submerged in electrolyte together with a negative platinum needle-shaped electrode and a reference electrode. The silver halide particles on the filter paper are slowly scanned individually with the needle-shaped electrode, whereupon the silver halide grains are individually electrochemically reduced at the cathode. This electrochemical reduction is accompanied by a current pulse, which is registered as a function of time and integrated to give the charge transfer Q for the electrochemical reduction of the silver halide particle, which is proportional to its volume. From their volume the equivalent circular grain diameter of each grain can be determined and therefrom the average particle size and size distribution.
A process for producing an aqueous dispersion is provided by the instant invention comprising: preparing a dispersion of photosensitive silver halide and a binder or a surfactant in an aqueous medium; and subsequently either (a) adding a first silver salt to the silver halide dispersion and then adding a second silver salt; or (b) adding the second silver salt to the silver halide dispersion and then adding the first silver salt, wherein the aqueous dispersion is substantially free of a water-soluble metal or ammonium salt of an aliphatic carboxylic acid with greater than 12 carbon atoms, the first silver salt is a substantially light-insensitive and substantially water-insoluble silver salt of an organic carboxylic acid, and the second silver salt has a water-solubility greater than 0.1 g in 1 L of water at 20xc2x0 C.
In the process of the present invention incorporating option (a) it is preferred that the silver behenate not be prepared in the presence of silver halide.
Such processes exclude the synthesis process of the first silver salt as can be seen from the absence from the aqueous dispersion of a metal or ammonium salt of an aliphatic carboxylic acid with greater than 12 carbon atoms.
The binder used for dispersing the photosensitive silver halide may a water-dispersible or a water-soluble binder. Suitable water-soluble binders are: polyvinyl alcohol, polyacrylamide, polymethacrylamide, polyacrylic acid, polymethacrylic acid, polyethyleneglycol, polyvinylpyrrolidone, proteinaceous binders such as gelatine, modified gelatines such as phthaloyl gelatine, polysaccharides, such as starch, gum arabic and dextran and water-soluble cellulose derivatives.
The surfactant used for dispersing the photosensitive silver halide is preferably a anionic or non-ionic surfactant, with anionic sulfonate surfactants being particularly preferred.
In a preferred embodiment of the process for producing an aqueous dispersion incorporating option (b), according to the present invention, there is an increase in UAg between step (i) and step (ii), UAg being the potential difference between a silver electrode (of xe2x89xa799.99% purity) in the aqueous liquid and a reference electrode consisting of a Ag/AgCl-electrode in 3M KCl solution at room temperature connected with the liquid via a salt bridge consisting of a 10% KNO3 salt solution. The UAg increase due to adding the second silver salt is preferably at least 50 mV, with at least 100 mV being particularly preferred.
In a further preferred embodiment of the process for producing an aqueous dispersion incorporating option (b), according the present invention, there is an decrease in UAg between step (ii) and step (iii), UAg being the potential difference between a silver electrode (of xe2x89xa799.99% purity) in the aqueous liquid and a reference electrode consisting of a Ag/AgCl-electrode in 3M KCl solution at room temperature connected with the liquid via a salt bridge consisting of a 10% KNO3 salt solution.
In a still further preferred embodiment of the process for producing an aqueous dispersion, according to the present invention, aqueous ammonia is added such that the pH of the aqueous dispersion does not exceed a value of 9.0. At higher pH-values silver hydroxide and silver oxide are formed, which cause increased image background (Dmin) levels.
According to the processes for producing an aqueous emulsion according to the present invention the second silver salt can be added as an aqueous solution, dissolved in a small quantity of water-miscible organic solvent or as a slurry in water, although in the latter case the particles of second silver salt must dissolve during the production of the aqueous emulsion.
The water-solubility of the second silver salt mainly influences the preparation time of the aqueous dispersion, since the increase in photosensitivity is dependent upon ionic dissociation of the second silver salt in the aqueous medium. The water-solubility of the second silver salt is therefore greater than 0.1 g in 1 L of water at 20xc2x0 C.
The binder or surfactant is necessary to keep the substantially light-insensitive and water insoluble organic silver salt and the photosensitive silver halide in suspension.
In a preferred embodiment of the process for preparing an aqueous dispersion, according to the present invention, the second silver salt is selected from the group consisting of silver nitrate, silver acetate, silver lactate and silver sulphate.
The present invention provides an aqueous dispersion obtainable by the above-mentioned processes for preparing an aqueous dispersion.
In a preferred embodiment of the aqueous dispersion, according to the present invention, the quantity of second silver salt added is at least 1 mol % with respect to the quantity of the photosensitive silver halide and preferably at least 15 mol % with respect to the quantity of the photosensitive silver halide. The quantity of second silver salt is preferably also less than 80 mol % with respect to the quantity of the photosensitive silver halide. The particle size of the photosensitive silver halide is preferably between 70 and 100 nm.
In a still further preferred embodiment of the aqueous dispersion according to the present invention, the aqueous dispersion further contains a reducing agent for the first silver salt.
Suitable organic reducing agents for the reduction of the first silver salt particles are organic compounds containing at least one active hydrogen atom linked to O, N or C, such as is the case with: aromatic di- and tri-hydroxy compounds; aminophenols; METOL(trademark); p-phenylene-diamines; alkoxynaphthols, e.g. 4-methoxy-1-naphthol described in U.S. Pat. No. 3,094,41; pyrazolidin-3-one type reducing agents, e.g. PHENIDONE(trademark); pyrazolin-5-ones; indan-1,3-dione derivatives; hydroxytetrone acids; hydroxytetronimides; hydroxylamine derivatives such as for example described in U.S. Pat. No. 4,082,901; hydrazine derivatives; and reductones e.g. ascorbic acid; see also U.S. Pat. Nos. 3,074,809, 3,080,254, 3,094,417 and 3,887,378. Particularly suitable reducing agents are sterically hindered phenols, bisphenols, sulfonamidophenols and those described in WO97/04357.
Combinations of reducing agents may also be used that on heating become reactive partners in the reduction of the substantially light-insensitive silver salt of an organic carboxylic acid. For example, combinations of sterically hindered phenols with sulfonyl hydrazide reducing agents such as disclosed in U.S. Pat. No. 5,464,738; trityl hydrazides and formyl-phenyl-hydrazides such as disclosed in U.S. Pat. No. 5,496,695; trityl hydrazides and formyl-phenyl-hydrazides with diverse auxiliary reducing agents such as disclosed in U.S. Pat. No. 5,545,505, U.S. Pat. No. 5,545,507 and U.S. Pat. No. 5,558,983; acrylonitrile compounds as disclosed in U.S. Pat. No. 5,545,515 and U.S. Pat. No. 5,635,339; and 2-substituted malonodialdehyde compounds as disclosed in U.S. Pat. No. 5,654,130
According to the present invention, the photothermographic recording material thermally developable under substantially water-free conditions of the present invention comprises a support and a photo-addressable thermally developable element, which fulfills two requirements: (i) it contains a first silver salt, a reducing agent therefor in thermal working relationship therewith, a photosensitive silver halide and a binder; and (ii) it comprises a layer obtainable by coating an aqueous dispersion, according to the present invention.
These two requirements will overlap in that the aqueous dispersion contains a binder or a surfactant, a first silver salt, a photosensitive silver halide, a second silver salt and optionally contains a reducing agent for the first silver salt, a spectral sensitizer, a supersensitizer, one or more stabilizers and a binder.
The photo-addressable thermally developable element may comprise a single layer, i.e. produced with the aqueous dispersion according to the present invention, or may comprise more than one layer, one of which is produced with the aqueous dispersion and the others containing the other ingredients necessary for image formation e.g. a reducing agent for the first silver salt, a binder, a toning agent and one or more stabilizers. In this layer system the photosensitive silver halide should be in catalytic association with the substantially light-insensitive silver salt of an organic carboxylic acid, the spectral sensitizer should be optionally together with a supersensitizer in intimate sensitizing association with the silver halide particles and the other ingredients active in the thermal development process or pre- or post-development stabilization of the element should be in the same layer or in other layers with the proviso that the organic reducing agent and the toning agent, if present, should be in thermal working relationship with the substantially light-insensitive silver salt of an organic carboxylic acid i.e. during the thermal development process the reducing agent and the toning agent, if present, are able to diffuse to the substantially light-insensitive silver salt of an organic carboxylic acid. The photo-addressable thermally developable element may also be coated with a protective layer.
The film-forming binder for use in the aqueous dispersion and photo-addressable thermally developable element of the present invention may a water-dispersible or a water-soluble binder.
Suitable water-soluble film-forming binders are: polyvinyl alcohol, polyacrylamide, polymethacrylamide, polyacrylic acid, polymethacrylic acid, polyethyleneglycol, polyvinylpyrrolidone, proteinaceous binders such as gelatine, modified gelatines such as phthaloyl gelatine, polysaccharides, such as starch, gum arabic and dextran and water-soluble cellulose derivatives.
Suitable water-dispersible binders are any water-insoluble polymers e.g. water-insoluble cellulose derivatives, polyurethanes, polyesters polycarbonates and polymers derived from xcex1,xcex2-ethylenically unsaturated compounds such as after-chlorinated polyvinyl chloride, partially hydrolyzed polyvinyl acetate, polyvinyl acetals, preferably polyvinyl butyral, and homopolymers and copolymers produced using monomers selected from the group consisting of: vinyl chloride, vinylidene chloride, acrylonitrile, acrylamides, methacrylamides. methacrylates, acrylates, methacrylic acid, acrylic acid, vinyl esters, styrenes, dienes and alkenes; or mixtures thereof.
Preferred water-dispersible binders are water-dispersible film-forming polymers with covalently bonded ionic groups selected from the group consisting of sulfonate, sulfinate, carboxylate, phosphate, quaternary ammonium, tertiary sulfonium and quaternary phosphonium groups. Further preferred water-dispersible binders are water-dispersible film-forming polymers with covalently bonded moieties with one or more acid groups.
It should be noted that, in the case of very small polymer particles, there is no clear cut transition between a polymer dispersion and a polymer solution.
Water-dispersible binders with crosslinkable groups, e.g. epoxy groups, aceto-acetoxy groups and crosslinkable double bonds are also preferred. Preferred water-dispersible binders for use in the photo-addressable thermally developable element of the present invention are polymer latexes as disclosed in WO 97/04355.
The above mentioned binders or mixtures thereof may be used in conjunction with waxes or xe2x80x9cheat solventsxe2x80x9d also called xe2x80x9cthermal solventsxe2x80x9d or xe2x80x9cthermosolventsxe2x80x9d improving the reaction speed of the redox-reaction at elevated temperature.
The aqueous dispersion or photo-addressable thermally developable element of the photothermographic recording material, according to the present invention, may contain a spectral sensitizer, optionally together with a supersensitizer, for the silver halide appropriate for the wavelength of the light source which may in the near UV, visible, e.g. 630 nm, 670 nm etc., or IR, parts of spectrum. The silver halide may be spectrally sensitized with various known dyes including cyanine, merocyanine, styryl, hemicyanine, oxonol, hemioxonol and xanthene dyes optionally, particularly in the case of sensitization to infra-red radiation, in the presence of a so-called supersensitizer. Useful cyanine dyes include those having a basic nucleus, such as a thiazoline nucleus, an oxazoline nucleus, a pyrroline nucleus, a pyridine nucleus, an oxazole nucleus, a thiazole nucleus, a selenazole nucleus and an imidazole nucleus. Useful merocyanine dyes which are preferred include those having not only the above described basic nuclei but also acid nuclei, such as a thiohydantoin nucleus, a rhodanine nucleus, an oxazolidinedione nucleus, a thiazolidinedione nucleus, a barbituric acid nucleus, a thiazolinone nucleus, a malononitrile nucleus and a pyrazolone nucleus. In the above described cyanine and merocyanine dyes, those having imino groups or carboxyl groups are particularly effective.
According to the present invention the aqueous dispersion or photo-addressable thermally developable element may further include a supersensitizer. Preferred supersensitizers are selected from the group of compounds consisting of: mercapto-compounds, disulfide-compounds, stilbene compounds, organoborate compounds and styryl compounds.
In order to obtain a neutral black image tone in the higher densities and neutral grey in the lower densities, the aqueous dispersion or photo-addressable thermally developable element according to the present invention may contain one or more toning agents. The toning agents should be in thermal working relationship with the first silver salt and reducing agent therefor during thermal processing.
In order to obtain improved shelf-life and reduced fogging, stabilizers and antifoggants such as phenyl tribromomethyl sulphone, 4-methyl phthalic acid and 2-mercapto-4-heptyl-oxadiazole may be incorporated into the photo-addressable thermally developable elements or the aqueous dispersion of the present invention.
The support for the photothermographic recording material according to the present invention may be transparent, translucent or opaque and is preferably a thin flexible carrier made e.g. from paper, polyethylene coated paper or transparent resin film, e.g. made of a cellulose ester, e.g. cellulose triacetate, polypropylene, polycarbonate or polyester, e.g. polyethylene terephthalate. The support may be in sheet, ribbon or web form. The support may be subbed with a subbing layer. It may also be made of an opacified resin composition.
The photothermographic recording materials used in the present invention may also contain antihalation or acutance dyes which absorb light which has passed through the photosensitive thermally developable photographic material, thereby preventing its reflection. Such dyes may be incorporated into the photo-addressable thermally developable element or in any other layer of the photothermographic material of the present invention.
In a preferred embodiment the photothermographic recording material of the present invention an antistatic layer is applied to is an outermost layer.
Surfactants are surface active agents which are soluble compounds which reduce the interfacial tension between a liquid and a solid. The thermographic and photothermographic recording materials of the present invention may contain anionic, non-ionic or amphoteric surfactants, with anionic and non-ionic surfactants preferred as disclosed in WO 97/04356. Suitable dispersants are natural polymeric substances, synthetic polymeric substances and finely divided powders, for example finely divided non-metallic inorganic powders such as silica.
The coating of any layer of the photothermographic recording materials of the present invention may proceed by any coating technique e.g. such as described in Modern Coating and Drying Technology, edited by Edward D. Cohen and Edgar B. Gutoff, (1992) VCH Publishers Inc., 220 East 23rd Street, Suite 909 New York, N.Y. 10010, USA, hereby incorporated by reference.
The present invention also provides a process for preparing a photothermographic recording material.
Surprisingly it has been found that by subjecting the photothermographic recording materials, produced according to the above-mentioned process, to temperatures at or above 35xc2x0 C. in the dark for at least 3 days, there is little or no change in background density Dmin and S-value and moreover that the Dmin- and S-values had been stabilized, as evidenced by the little or no additional change in Dmin- and S-values upon storage in the dark under conditions such as 7 days at 45xc2x0 C. and 70% relative humidity, which simulate prolonged shelf-life conditions, whether the photothermographic recording material was present as a roll of material or as individual sheets.
In a preferred embodiment of the process for preparing a photothermographic recording material the thermographic recording material is heated at a temperature of at least 35xc2x0 C. for at least 3 days with a temperature of at least 45xc2x0 C. being particularly preferred. Furthermore, the temperature is preferably less than 50xc2x0 C. The period is preferably at least 1 week and the heating is preferably carried out at a relative humidity between 10 and 75% and particularly preferably between 15 and 70%. Especially preferred is heating in the dark for 7 days at 45xc2x0 C. and 70% relative humidity.
Photothermographic recording materials, according to the present invention, may be exposed with radiation of wavelength between an X-ray wavelength and a 5 microns wavelength with the image either being obtained by pixel-wise exposure with a finely focused light source, such as a CRT light source; a UV, visible or IR wavelength laser, such as a He/Ne-laser or an IR-laser diode, e.g. emitting at 780 nm, 830 nm or 850 nm; or a light emitting diode, for example one emitting at 659 nm; or by direct exposure to the aspect itself or an image therefrom with appropriate illumination e.g. with UV, visible or IR light. For the thermal development of image-wise exposed photothermographic recording materials, according to the present invention, any sort of heat source can be used that enables the recording materials to be uniformly heated to the development temperature in a time acceptable for the application concerned e.g. contact heating, radiative heating, microwave heating etc.
Photothermographic recording materials according to the present invention may be used for both the production of transparencies, for example in the medical diagnostic field in which black-imaged transparencies are widely used in inspection techniques operating with a light box, reflection type prints, for example in the hard copy graphics field and in microfilm applications. For such applications the support will be transparent or opaque, i.e. having a white light reflecting aspect. Should a transparent base be used, the base may be colourless or coloured, e.g. with a blue colour for medical diagnostic applications.